In order to engage an enemy in combat you must let them see you so you can fight them. In order to fight you press [ Register or Signin to view external links. ] for normal attack and [ Register or Signin to view external links. ] for a heavy attack. Some enemies can only be defeated in certain ways which you will learn via small tutorials as you progress through the game. You will unlikely unlock this by the end of your first playthrough as you should be focusing on assassination and shadow kills.

A good place to grind this trophy post game, along with Enemy Of My Enemy and I Fear No One is just after the first gate in Memory Sequence 6: The Search. Alert the enemies to the right and then move to the left to see another 3 guards appear. You should then block the enemy's attack and activate Helix Kills by pressing [ Register or Signin to view external links. ] + [ Register or Signin to view external links. ] . This way you will work towards 2-3 trophies at one time.
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